Two substorm intensifications compared: Onset, expansion, and global consequences

T. I. Pulkkinen*, D. N. Baker, L. A. Frank, J. B. Sigwarth, H. J. Opgenoorth, R. Greenwald, E. Friis-Christensen, T. Mukai, R. Nakamura, H. Singer, G. D. Reeves, M. Lester

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

32 Citations (Scopus)


We present observations of two sequential substorm onsets on May 15, 1996. The first event occurred during persistently negative IMF Bz, whereas the second expansion followed a northward turning of the interplanetary magnetic field (IMF). While the first onset remained localized, the second event led to a major reconfiguration of the magnetotail. The two very different events are contrasted, and it is suggested that the IMF direction controls the evolution of the expansion phase after the initial onset. Magnetic field modeling and field-aligned mappings are used to find the high-altitude source region of the auroral features and currents giving rise to ground magnetic disturbances: It is shown that the auroral brightening is related to processes near the inner edge of the plasma sheet but that the initial field-aligned currents couple to the midtail region. Ground magnetograms show an abrupt, large-scale weakening of the electrojet during the recovery phase. This event is followed by eastward drifting omega bands in a double-oval configuration. During that period, the Geotail plasma data show oscillations at

Original languageEnglish
Article number97JA01985
Pages (from-to)15-27
Number of pages13
JournalJournal of geophysical research: Space physics
Issue numberA1
Publication statusPublished - 1998
MoE publication typeA1 Journal article-refereed


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